Friday, 24 July 2015

Caves hold clues to past climate... by Laura Deeprose

Laura entering the cave; getting in and out is a tight squeeze!

Often people look at stalagmites and stalactites within caves and admire their strange shapes and fascinating formations. However, the slow and systematic growth of these cave deposits, referred to as speleothems, can also reveal a vast amount of information about climate from hundreds of thousands of years ago to the modern day. Speleothems are formed by water from rainfall moving through the soil, bedrock and then into the cave. The chemistry of these drip waters reflects the climatic and environmental conditions of the time and therefore the chemistry of speleothems can be analysed to reconstruct past climatic and environmental changes over time. Here Laura Deeprose, a PhD student with Lancaster University and the British Geological Survey tells us more about her exciting research…

My PhD project is focussed on producing a record of past climatic and environmental change between 50,000 – 30,000 years ago in the northern Iberian Peninsula. It was during this period that the last Neanderthals disappeared from our planet and it is believed by some that their demise was related to changes in climate. During this time period a series of abrupt and severe climatic events are known to have occurred across the Northern Hemisphere. These events, known as Heinrich Events, led to widespread cooling and aridity across the Northern Hemisphere, with each event lasting approximately 1000 years.

Perlas Cave is home to countless
stalagmites and stalactites

Speleothem sample from Perlas Cave after being cut at BGS

Currently, there are few climate reconstructions from areas where the last Neanderthals survived, such as the Iberian Peninsula and those that do exist don't have a high enough resolution to assess the climatic and environmental impacts associated with these events. A key advantage of using speleothems in palaeoclimate reconstruction is their potential to be accurately dated by uranium-series dating. Uranium is dissolved into solution as water moves through the bedrock and incorporated into speleothem calcite during growth. The subsequent radioactive decay of the uranium to thorium acts like a radioactive clock and can provide us with an accurate and precise age for a given layer of calcite within a speleothem.

After nine months of working on this project I have established a cave monitoring regime in Cueva de las Perlas (northern Iberia) to determine how the climate signal is being transferred into modern speleothem calcite. In addition, I have drilled and sampled numerous speleothems for uranium-series dating. After the dates come back we will select speleothems of appropriate age for further geochemical analyses including oxygen and carbon isotopes, further uranium-series dating and trace elements. All the geochemistry is being done at the British Geological Survey.

Laura is a PhD student at Lancaster University, supervised by Dr Peter Wynn and Prof Phil Barker and at the BGS supervised by Prof Melanie Leng and Dr Stephen Noble